1. Field of the Invention
The present invention relates to: a fluorescent substance that is excited by light having a predetermined wavelength to emit light; a light-emitting diode including the fluorescent substance, provided with an enclosing portion for enclosing a light-emitting diode (hereafter referred to as LED) chip and used for displays, illumination, LCD backlights or the like; and a method for producing the fluorescent substance.
2. Description of Related Art
An LED, a light-emitting device, is compact, capable of emitting bright color light efficiently, excellent in drive characteristics, and highly resistant against vibration and repeated ON/OFF lighting. For these reasons, it is used as various indicators and various light sources.
As LED chips serving as semiconductor light-emitting devices, LED chips emitting light of various colors have become commercially practical, for example, short-wavelength LED chips including a GaN-based semiconductor as a luminous layer to emit light of colors, such as ultraviolet, blue and cyan, and high-luminance red LED chips. For example, an LED lamp capable of emitting light of various colors, wherein three LED chips, blue, red and green, for example, are mounted to produce colors by adjusting the brightness of each LED chip, have also become commercially practical and is used for full color displays and the like. In addition, an LED lamp capable of emitting white light, obtained by mounting a plurality of LED chips in one lamp or by combining an LED chip with a fluorescent substance, is expected as a future illumination light source.
Available LEDs wherein the color of the light emitted from an LED chip is converted by a fluorescent substance are LEDs described in, for example, Japanese Patent No. 2927279 and Japanese Patent No. 3246386. In these LEDs, the color of the light emitted from one kind of LED chip can be converted into white or the like by including a YAG (Y3Al5O12):Ce-based fluorescent substance in an enclosing portion, made of synthetic resin, for enclosing an LED chip.
However, in the case where an LED is produced by including the above-mentioned YAG:Ce-based fluorescent substance in the LED chip enclosing portion, the luminous intensity and the luminous efficiency of the LED are insufficient. It is therefore requested to develop a fluorescent substance that can enhance the luminous intensity and the luminous efficiency and can decrease the power consumption of the LED.
Furthermore, since the fluorescent substance is exposed to high-energy light emitted from the LED chip, it deteriorates with time and blackens, thereby causing problems of making color conversion nonuniform, making the light emission of the LED nonuniform and lowering the extraction efficiency of the light emitted from the LED. In the case where moisture enters the interior of the enclosing portion, the deterioration of the fluorescent substance is accelerated by the high-energy light, heat and the like from the LED chip, whereby the above-mentioned problems are apt to occur more frequently. It is therefore requested to develop a fluorescent substance that hardly reacts with moisture and does not deteriorate with time.